Experimental determination of superconducting parameters for the intermetallic perovskite superconductor MgCNi ₃

We have measured upper-critical-field H_c2, specific heat C, and tunneling spectra of the intermetallic perovskite superconductor MgCNi₃ with a superconducting transition temperature T_c,≈7.6 K. Based on these measurements and relevant theoretical relations, we have evaluated various superconducting parameters for this material, including the thermodynamic critical field H_c(0), coherence length ξ(0), penetration depth λ(0), lower-critical-field H_c1(0), and Ginzburg-Landau parameter κ(0). From the specific heat, we obtain the Debye temperature Θ_D≈284 K. We find ajump of ΔClλT_c=2.1 at T_c (where γ is the normal-state electronic specific coefficient), which is larger than the weak-coupling BCS value of 1.43, suggesting that MgCNi₃ may be a strong-coupling superconductor. In addition, we observed a pronounced zero-bias conductance peak (ZBCP) in the tunneling spectra. We discuss the possible physical origins of the observed ZBCP.